U.S. patent application number 13/169964 was filed with the patent office on 2011-12-29 for image processing apparatus and image forming apparatus.
Invention is credited to Masaya Fujitani, Takashi Kitagawa, Katsuhiro Nagayama, Masayuki Otsuka, Norihide YASUOKA.
Application Number | 20110317221 13/169964 |
Document ID | / |
Family ID | 45352303 |
Filed Date | 2011-12-29 |
![](/patent/app/20110317221/US20110317221A1-20111229-D00000.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00001.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00002.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00003.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00004.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00005.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00006.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00007.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00008.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00009.png)
![](/patent/app/20110317221/US20110317221A1-20111229-D00010.png)
United States Patent
Application |
20110317221 |
Kind Code |
A1 |
YASUOKA; Norihide ; et
al. |
December 29, 2011 |
IMAGE PROCESSING APPARATUS AND IMAGE FORMING APPARATUS
Abstract
An image processing section includes a density correction
adjustment section, and in response to an instruction from a
density correction process section to adjust a density correction
process, the density correction adjustment section reviews a
conversion value table which is used by the density correction
process section to calculate an output correction value by
conversion, so as to adjust the density correction process.
Inventors: |
YASUOKA; Norihide;
(Osaka-shi, JP) ; Otsuka; Masayuki; (Osaka-shi,
JP) ; Fujitani; Masaya; (Osaka-shi, JP) ;
Nagayama; Katsuhiro; (Osaka-shi, JP) ; Kitagawa;
Takashi; (Osaka-shi, JP) |
Family ID: |
45352303 |
Appl. No.: |
13/169964 |
Filed: |
June 27, 2011 |
Current U.S.
Class: |
358/3.06 |
Current CPC
Class: |
H04N 1/4078 20130101;
H04N 1/6033 20130101; G03G 15/011 20130101; H04N 1/6036
20130101 |
Class at
Publication: |
358/3.06 |
International
Class: |
H04N 1/405 20060101
H04N001/405 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2010 |
JP |
2010-146314 |
Claims
1. An image forming apparatus having a function of carrying out a
plurality of halftone processes, the image forming apparatus
comprising: a density correction process section for carrying out a
density correction process with respect to the plurality of
halftone processes; and a density correction adjustment section for
adjusting the density correction process carried out by the density
correction process section, the density correction process section
finding an output correction value of a reference halftone process
of the plurality of halftone processes by use of a result of
measurement of densities of respective patches of a patch pattern
subjected to the reference halftone process, and finding an output
correction value of at least one of the plurality of halftone
processes which is other than the reference halftone process by
conversion from the output correction value of the reference
halftone process by use of a conversion parameter set for the at
least one halftone process, the density correction adjustment
section receiving an instruction to adjust the density correction
process carried out by the density correction process section and
reviewing the conversion parameter used by the density correction
process section, so as to adjust the density correction
process.
2. The image forming apparatus as set forth in claim 1, wherein:
the density correction adjustment section includes: a first output
correction value actual measurement section for, in response to an
instruction to adjust a halftone process of the plurality of
halftone processes which is other than the reference halftone
process, finding an output correction value of the halftone process
by use of a result of measurement of densities of respective
patches of a patch pattern subjected to the halftone process whose
adjustment has been instructed; a first conversion parameter
calculation section for, in accordance with (i) the output
correction value found by the first output correction value actual
measurement section and (ii) the output correction value of the
reference halftone process already found by the density correction
process section, finding a new conversion parameter for the
halftone process whose adjustment has been instructed; and a first
conversion parameter update section for updating a conversion
parameter of the halftone process whose adjustment has been
instructed to the new conversion parameter calculated by the first
conversion parameter calculation section.
3. The image forming apparatus as set forth in claim 1, wherein:
the density correction adjustment section includes: a second output
correction value actual measurement section for, in response to an
instruction to adjust the reference halftone process of the
plurality of halftone processes, finding an output correction value
of the reference halftone process by use of the result of the
measurement of the densities of the respective patches of the patch
pattern subjected to the reference halftone process; a second
conversion parameter calculation section for finding new conversion
parameters for all the halftone processes having conversion
parameters in accordance with (i) the output correction value of
the reference halftone process found by the second output
correction value actual measurement section, (ii) the output
correction value of the reference halftone process already found by
the density correction process section, and (iii) predetermined
conversion parameters so that an output correction value found by
conversion from the output correction value of the reference
halftone process found by the second output correction value actual
measurement section is identical to an output correction value
found by conversion from the output correction value of the
reference halftone process already found by the density correction
process section; and a second conversion parameter update section
for updating the conversion parameters of all the halftone
processes to the new conversion parameters calculated by the second
conversion parameter calculation section.
4. The image forming apparatus as set forth in claim 1, further
comprising a reference halftone process changing section which
enables a change of reference halftone processes in the density
correction process section.
5. The image forming apparatus as set forth in claim 4, further
comprising: a counting section for measuring a frequency of use, in
a given period, of the plurality of halftone processes, each being
a possible reference halftone process, the reference halftone
process changing section setting, as a reference halftone process,
a halftone process of the plurality of halftone processes whose
frequency of use measured by the counting section is the
highest.
6. The image forming apparatus as set forth in claim 1, wherein the
conversion parameter is a conversion value.
7. The image forming apparatus as set forth in claim 6, wherein the
conversion value is a difference from or a ratio to the output
correction value of the reference halftone process.
8. An image forming apparatus comprising an image processing
apparatus recited in claim 1.
9. A non-transitory computer-readable recording medium in which a
program is recorded for causing a computer to function as each
section of an image processing apparatus recited in claim 1.
Description
[0001] This Nonprovisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No. 2010-146314 filed in
Japan on Jun. 28, 2010, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to an image processing
apparatus for carrying out a density correction with respect to an
image forming apparatus. More specifically, the present invention
relates to (i) an image processing apparatus which has a function
of carrying out a plurality of halftone processes, carries out a
density correction by actual measurement with respect to only one
of the plurality of halftone processes that is required to be
subjected to the density correction, and carries out the density
correction with respect to the other halftone processes by
conversion from a result of the density correction by actual
measurement carried out with respect to the only one halftone
process and (ii) an image forming apparatus including the image
processing apparatus.
BACKGROUND ART
[0003] Conventionally, a display device which has a resolution of
approximately 75 dpi (Dot Per Inch) to 100 dpi is commonly used for
a personal computer (hereinafter, referred to as a PC). In
contrast, as for a resolution of an image forming apparatus, an
electrophotographic printer has a resolution of approximately 600
dpi to 2400 dpi, and an inkjet printer has a resolution of
approximately 360 dpi to 2880 dpi. This shows that an image forming
apparatus has a higher resolution than a PC display device.
[0004] As for gradation, a PC display device provides 256-level
gray scale for each of RGB. In contrast, an image forming apparatus
providing two-level gray scale is commonly used, and an image
forming apparatus provides approximately 64-level gray scale at
most. Even an image forming apparatus providing approximately
64-level gray scale often fails to appropriately express gradation
in a low-density part and a high-density part of a printed
image.
[0005] As described earlier, a PC display device which displays a
digital image and an image forming apparatus which prints the
digital image greatly differ mainly in resolution and
gradation.
[0006] Therefore, in order to absorb a difference in gradation, an
image forming apparatus carries out a halftone process (also
referred to as a gradation reproduction process or quantization
means) such as a dither method or an error diffusion method in
printing a digital image. Such a halftone process has a
characteristic of obtaining gradation in exchange for resolution or
obtaining resolution in exchange for gradation. The image forming
apparatus properly uses a plurality of halftone processes in
accordance with a type of a digital image to be printed.
[0007] For example, in order to print a text, the image forming
apparatus carries out a halftone process which places greater
importance on reproduction of resolution than on reproduction of
gradation. In contrast, in order to print a photograph, the image
forming apparatus carries out a halftone process which places
greater importance on reproduction of gradation than on
reproduction of resolution. In this case, it is known that a shape
(a curved line) of a density characteristic to be reproduced varies
depending on a kind and/or a setting of a halftone process.
[0008] FIG. 10 is a graph illustrating density characteristics of
respective halftone processes. The density characteristics of the
respective halftone processes differ among the halftone processes.
For example, a halftone process for providing a high resolution
such as an error diffusion method or a high lpi (line per inch)
dither method has a density characteristic which is close to a
density characteristic of an image forming apparatus itself. In
contrast, a halftone process for providing a low resolution such as
a low lpi dither method tends to have a density characteristic
which is close to a straight line (an ideal density
characteristic). Note that a curved line which shows such a density
characteristic of a halftone process changes over time depending
on, for example, conditions such as temperature and humidity, and a
usage state.
[0009] Therefore, an image forming apparatus having a function of
carrying out a plurality of halftone processes carries out process
control so as to keep a printing density and a color tone constant
among the plurality of halftone processes. Then, the image forming
apparatus carries out a density correction with respect to each of
the plurality of halftone processes. The process control, which is
an image quality adjustment for achieving both user convenience and
a stable image quality, is carried out at turn-on, when a change
over time or an environmental change is detected, or at a timing at
which the number of sheets printed reaches a given number.
[0010] Patent Literature 1 discloses a density correction method.
According to the density correction method, an arrangement having a
function of carrying out plurality of halftone processes carries
out a density correction by forming toner patches for all halftone
processes that are required to be subjected to the density
correction and actually measuring patch densities of the toner
patches.
[0011] However, according to the density correction method of
Patent Literature 1, actual patch density measurement is carried
out with respect to each of the halftone processes that is required
to be subjected to the density correction. Therefore, this causes
problems of (i) costs for materials to be consumed (e.g., toner and
ink) and (ii) longer time required for the density correction.
[0012] Patent Literature 2 proposes a density correction method
such that one of a plurality of halftone processes is set as a
reference halftone process, a density correction is carried out
with respect to only the reference halftone process by actual patch
density measurement, and the density correction is carried out with
respect to the other halftone processes by conversion from an
output correction value of the reference halftone process (a result
of the density correction carried out with respect to the reference
halftone process).
[0013] Patent Literature 2 can solve the problems of Patent
Literature 1. This is because according to Patent Literature 2, an
output correction value is found by carrying out actual patch
density measurement with respect to only the reference halftone
process, and merely conversion from the output correction value of
the reference halftone process is carried out with respect to the
other halftone processes.
Citation List
[0014] Patent Literature 1 [0015] Japanese Patent Application
Publication, Tokukai, No. 2002-374416 A (Publication Date: Dec. 26,
2002)
[0016] Patent Literature 2 [0017] Japanese Patent Application
Publication, Tokukai, No. 2005-144883 A (Publication Date: Jun. 9,
2005)
SUMMARY OF INVENTION
Technical Problem
[0018] However, the density correction method of Patent Literature
2 is designed such that a conversion value, which is fixed, cannot
be reviewed in carrying out the density correction by conversion
from the output correction value of the reference halftone
process.
[0019] Therefore, for a halftone process in which a density
correction is carried out by use of a conversion value, the density
correction method of Patent Literature 2 fails to respond to a case
where a change over time in density characteristic of the halftone
process occurs or an abnormality in the halftone process is
indicated.
[0020] It is desirable that a conversion value be set for each
device in view of an individual difference between devices.
However, a common conversion value set in accordance with actual
measurement may be set for devices of an identical model in terms
of cost. In a case where a density correction is carried out by use
of a fixed common conversion value, the density correction method
of Patent Literature 2 also fails to respond to such an individual
difference between devices.
[0021] The present invention has been made in view of the problems,
and an object of the present invention is to make (i) an image
processing apparatus in which a review of a conversion value and a
conversion expression can be carried out with respect to the other
halftone processes which are subjected to a density correction by
conversion in accordance with an output correction value of a
reference halftone process which has been subjected to the density
correction, so that the density correction is carried out with high
accuracy even by use of conversion, and (ii) an image forming
apparatus including the image processing apparatus.
Solution to Problem
[0022] In order to attain the object of the present invention, an
image forming apparatus having a function of carrying out a
plurality of halftone processes, the image forming apparatus
includes: a density correction process section for carrying out a
density correction process with respect to the plurality of
halftone processes; and a density correction adjustment section for
adjusting the density correction process carried out by the density
correction process section, the density correction process section
finding an output correction value of a reference halftone process
of the plurality of halftone processes by use of a result of
measurement of densities of respective patches of a patch pattern
subjected to the reference halftone process, and finding an output
correction value of at least one of the plurality of halftone
processes which is other than the reference halftone process by
conversion from the output correction value of the reference
halftone process by use of a conversion parameter set for the at
least one halftone process, the density correction adjustment
section receiving an instruction to adjust the density correction
process carried out by the density correction process section and
reviewing the conversion parameter used by the density correction
process section, so as to adjust the density correction
process.
[0023] According to the arrangement, the density correction
adjustment section receives an instruction to adjust the density
correction process carried out by the density correction process
section and reviews the conversion parameter used by the density
correction process section, so as to adjust the density correction
process.
[0024] According to this, also for a halftone process using a
conversion parameter, the conversion parameter can be reviewed
properly in accordance with a change over time in density
characteristic of the halftone process and/or an individual
difference between apparatuses. This enables enhancement of a
density correction accuracy.
[0025] Therefore, it is possible to make an image processing
apparatus which carries out a density correction process with
higher accuracy even by use of conversion as compared with a
conventional arrangement in which a density correction process is
carried out by use of a conversion parameter (a conversion value or
a conversion expression) which cannot be rewritten and is
fixed.
Advantageous Effects of Invention
[0026] As described earlier, the image processing apparatus in
accordance with the present invention includes the density
correction adjustment section receiving an instruction to adjust
the density correction process carried out by the density
correction process section and reviewing the conversion parameter
used by the density correction process section, so as to adjust the
density correction process.
[0027] Therefore, the present invention yields an effect of making
an image processing apparatus which carries out a density
correction process with higher accuracy even by use of conversion
as compared with a conventional arrangement in which a density
correction process is carried out by use of a conversion parameter
(a conversion value or a conversion expression) which cannot be
rewritten and is fixed.
BRIEF DESCRIPTION OF DRAWINGS
[0028] FIG. 1 is a block diagram illustrating an example of an
arrangement of an image processing section in accordance with an
embodiment of the present invention.
[0029] FIG. 2 is a cross-sectional view illustrating an example of
an arrangement of an image forming apparatus including the image
processing section illustrated in FIG. 1.
[0030] FIG. 3 illustrates an example of a conversion value table
stored in a conversion value table storage section illustrated in
FIG. 1.
[0031] FIG. 4 illustrates an example of a patch set.
[0032] FIG. 5 illustrates an example of a program for calculating a
conversion value to be stored in the conversion value table
illustrated in FIG. 3.
[0033] FIG. 6 is a flow chart illustrating how the image processing
section illustrated in FIG. 1 carries out a density correction
adjustment process when a density adjustment instruction is given
to the other halftone processes.
[0034] FIG. 7 is a flow chart illustrating how the image processing
section illustrated in FIG. 1 carries out the density correction
adjustment process when the density adjustment instruction is given
to a reference halftone process.
[0035] FIG. 8 is a block diagram illustrating an example of an
arrangement of an image processing section in accordance with
another embodiment of the present invention.
[0036] FIG. 9 is a flow chart illustrating how the image processing
section illustrated in FIG. 8 carries out a reference halftone
process changing process.
[0037] FIG. 10 is a graph illustrating density characteristics of
respective halftone processes.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0038] A first embodiment of the present invention is described
below with reference to FIGS. 1 through 7. The present embodiment
discusses an application of an image processing apparatus in
accordance with the present invention to an image forming
apparatus.
[0039] FIG. 2 is a cross-sectional view illustrating an example of
an arrangement of an image forming apparatus 100 including an image
processing section 20 in accordance with the present invention. In
accordance with image data read by the image forming apparatus 100
or received from outside, the image forming apparatus 100 forms a
multicolor or single color image on a given recording sheet which
is a recording material.
[0040] The image forming apparatus 100 includes an apparatus body
110 and an automatically document processing device 121 (see FIG.
2).
[0041] The apparatus body 110 mainly includes an exposure unit 1,
developing units 2, photoreceptor drums 3, cleaner units 4,
chargers 5, an intermediate transfer belt unit 6, a fixing unit 7,
a paper feeding cassette 81, a document reading device 90, and a
paper output tray 91. The apparatus body 110 further includes the
image processing section (image processing apparatus) 20 (see FIG.
1).
[0042] A platen 92 which is made of transparent glass and on which
a document is placed is provided in an upper part of the apparatus
body 110, and the automatically document processing device 121 is
provided above the platen 92.
[0043] The automatically document processing device 121
automatically carries a document placed thereon to a reading
position located in a vicinity of the platen 92. The automatically
document processing device 121, which is rotatable about an axis
which is parallel to a horizontal direction of FIG. 2, is arranged
to uncover the platen 92, so that a document can be manually placed
on the platen 92.
[0044] The document reading device 90 reads a document placed on
the platen 92 or a document automatically carried to the reading
position in the vicinity of the platen 92. Then, an image forming
section 42 (see FIG. 1) receives image data indicative of an image
of the read document.
[0045] Image data handled by the image forming apparatus 100
correspond to color images of black (K), cyan (C), magenta (M), and
yellow (Y). Accordingly, the number of each of (i) the developing
units 2, (ii) the photoreceptor drums 3, (iii) the chargers 5, and
(iv) the cleaner units 4 is set to four so that four kinds of
latent images corresponding to the respective colors are formed. A
set of a developing unit 2, a photoreceptor drum 3, a charger 5,
and a cleaner unit 4 is provided for a corresponding one of black,
cyan, magenta, and yellow, so that four image forming stations are
provided.
[0046] The chargers 5 are charging devices for uniformly charging
top surfaces of the respective photoreceptor drums 3 at a given
electric potential. Not only a charger illustrated in FIG. 2 but
also a contact roller type charger or a brush type charger is
usable as each of the chargers 5.
[0047] The exposure unit 1, which corresponds to an image writing
device, is arranged as a laser scanning unit (LSU) mainly including
a laser emitting section and a reflection mirror. A polygon mirror
for scanning a laser beam and optical elements such as a lens and a
mirror for guiding, to the photoreceptor drums 3, laser light
reflected by the polygon mirror are provided in the exposure unit
1. Alternatively, for example, an arrangement using an EL or LED
write head in which light emitting devices are arranged in an array
pattern can be employed as the exposure unit 1.
[0048] The exposure unit 1 has a function of subjecting the
photoreceptor drums 3 thus charged to exposure in accordance with
image data received, so as to form static latent images on the top
surfaces of the respective photoreceptor drums 3 in accordance with
the image data.
[0049] The developing units 2 make the static latent images formed
on the respective photoreceptor drums 3 visible as toner images by
use of toners of four colors (YMCK).
[0050] The cleaner units 4 remove and collect the toners remaining
on the top surfaces of the respective photoreceptor drums 3 after
development and image transfer.
[0051] The intermediate transfer belt unit 6 provided above the
photoreceptor drums 3 includes an intermediate transfer belt 61, an
intermediate transfer belt driving roller 62, an intermediate
transfer belt driven roller 63, intermediate transfer rollers 64,
and an intermediate transfer belt cleaning unit 65. The number of
the intermediate transfer rollers 64 is set to four so that the
intermediate transfer rollers 64 correspond to the respective
colors of YMCK.
[0052] The intermediate transfer belt driving roller 62, the
intermediate transfer belt driven roller 63, and the intermediate
transfer rollers 64 stretch the intermediate transfer belt 61 so as
to rotatably drive the intermediate transfer belt 61. The
intermediate transfer rollers 64 apply transfer biases, so as to
transfer the toner images on the respective photoreceptor drums 3
onto the intermediate transfer belt 61.
[0053] The intermediate transfer belt 61 is provided so as to be in
contact with the photoreceptor drums 3. The intermediate transfer
belt unit 6 forms a color toner image (multicolor toner image)
thereon by sequentially superimposing the toner images of the
respective colors formed on the respective photoreceptor drums 3 on
the intermediate transfer belt 61 so as to transfer the toner
images. The intermediate transfer belt 61 is made of, for example,
a film having a thickness of approximately 100 .mu.m to 150 .mu.m
so as to have no end.
[0054] The intermediate transfer rollers 64 which are in contact
with a backside of the intermediate transfer belt 61 transfer the
toner images of the respective colors from the photoreceptor drums
3 onto the intermediate transfer belt 61. High-voltage transfer
biases (high voltages of polarity (+) reverse to charging polarity
(-) of toner) are applied to the respective intermediate transfer
rollers 64 so that the toner images are transferred onto the
intermediate transfer belt 61.
[0055] Each of the intermediate transfer rollers 64 is a roller
whose base is a metal (e.g., stainless) shaft having a diameter of
8 mm to 10 mm and whose top surface is covered with an
electroconductive elastic material (e.g., EPDM or urethane foam).
Such an electroconductive elastic material enables uniform
application of a high voltage to the intermediate transfer belt 61.
The present embodiment uses a roller type transfer electrode.
Alternatively, a brush type transfer electrode or the like is also
usable.
[0056] As described earlier, the toner images made visible on the
respective photoreceptor drums 3 in accordance with the respective
colors are stacked on the intermediate transfer belt 61. Rotation
of the intermediate transfer belt 61 causes information on the
images thus stacked to be transferred onto a recording sheet by a
transfer roller 10 (described later) provided in a part in which
the recording sheet and the intermediate transfer belt 61 are in
contact with each other.
[0057] In this case, the intermediate transfer belt 61 and the
transfer roller 10 are pressure-joined with a given nip, and a
voltage (a high voltage of polarity (+) reverse to charging
polarity (-) of toner) is applied to the transfer roller 10 so that
the toner images are transferred onto the recording sheet. Of the
transfer roller 10 and the intermediate transfer belt driving
roller 62, one is made of a rigid material (e.g., metal) and the
other is made of a flexible material (e.g., rubber or plastic
foam), so that the given nip is obtained steadily.
[0058] Toners which have been attached to the intermediate transfer
belt 61 due to their contact with the photoreceptor drums 3 and
remain on the intermediate transfer belt 61 without being
transferred onto the recording sheet by the transfer roller 10 may
cause a color mixture of the toners in a subsequent step.
Therefore, the intermediate transfer belt cleaning unit 65 removes
and collects the toners remaining on the intermediate transfer belt
61.
[0059] The intermediate transfer belt cleaning unit 65 includes a
cleaning member such as a cleaning blade which is in contact with
the intermediate transfer belt 61. The driven roller 63 supports,
from a backside of the intermediate transfer belt 61, a part of the
intermediate transfer belt 61 which part is in contact with the
cleaning blade.
[0060] A sensor (a detection section) 21 is provided to face a
surface of the intermediate transfer belt 61 on which surface toner
patches (described later) are formed. The sensor 21 is a reflective
sensor for detecting densities of the respective toner patches
formed on the intermediate transfer belt 61.
[0061] The paper feeding cassette 81, which is a tray in which
recording sheets to be used for image formation are accumulated, is
provided under the exposure unit 1 of the apparatus body 110.
Recording sheets to be used for image formation can also be placed
in a manual paper feeding cassette 82. The paper output tray 91
provided above the apparatus body 110 is a tray in which printed
recording sheets are accumulated facedown.
[0062] The apparatus body 110 has a recording sheet carrying path S
which is substantially vertical and through which the recording
sheets in the paper feeding cassette 81 and the manual paper
feeding cassette 82 are sent to the paper output tray 91 via the
transfer roller 10 and the fixing unit 7. Pickup rollers 11a and
11b, a plurality of carrying rollers 12a through 12d, a
registration roller 13, the transfer roller 10, the fixing unit 7,
etc. are provided in a vicinity of the recording sheet carrying
path S from the paper feeding cassette 81 or the manual paper
feeding cassette 82 to the paper output tray 91.
[0063] The plurality of carrying rollers 12a through 12d are small
rollers which are provided along the recording sheet carrying path
S so as to accelerate and assist carriage of recording sheets. The
pickup roller 11a, which is provided in a vicinity of an end of the
paper feeding cassette 81, picks up the recording sheets one by one
from the paper feeding cassette 81, so as to supply the recording
sheets thus picked up to the recording sheet carrying path S.
Similarly, the pickup roller 11b, which is provided in a vicinity
of an end of the manual paper feeding cassette 82, picks up the
recording sheets one by one from the manual paper feeding cassette
82, so as to supply the recording sheets thus picked up to the
recording sheet carrying path S.
[0064] The registration roller 13 temporarily holds a recording
sheet which is being carried through the recording sheet carrying
path S. The registration roller 13 carries the recording sheet to
the transfer roller 10 at a timing at which an end of a toner image
transferred onto the intermediate transfer belt 61 and a given part
of the recording sheet are positionally adjusted.
[0065] The fixing unit 7 includes a fixing roller 71 and a pressure
roller 72. The fixing roller 71 and the pressure roller 72 rotate
with a recording sheet sandwiched therebetween. The image forming
section 42 sets a temperature of the fixing roller 71 to not less
than a given fixing temperature in accordance with a signal from a
thermistor. The fixing roller 71 and the pressure roller 72 bond by
thermocompression unfixed toner with the recording sheet, so as to
melt, mix, and pressure-join the multicolor toner image transferred
onto the recording sheet and then heat fix the resulting image to
the recording sheet. A heater lump for heating the fixing roller 71
is provided in the fixing roller 71. Note that the fixing
temperature (given temperature) refers to a temperature at which a
fixing process can be carried out favorably.
[0066] The following description specifically discusses a recording
sheet carrying path. As described earlier, the paper feeding
cassette 81 and the manual paper feeding cassette 82 for storing
recording sheets are preliminarily provided in the image forming
apparatus 100. The pickup rollers 11a and 11b are provided for the
paper feeding cassettes 81 and 82, respectively so that the
recording sheets are fed from the paper feeding cassettes 81 and
82. The pickup rollers 11a and 11b guide the recording sheets one
by one to the recording sheet carrying path S.
[0067] Each of the recording sheets is carried from the paper
feeding cassette 81 or 82 to the registration roller 13 by the
carrying roller 12a provided in the recording sheet carrying path
S. The recording sheet is carried to the transfer roller 10 at a
timing at which a given part of the recording sheet and an end of
image information on the intermediate transfer belt 61 is
positionally adjusted, so that the image information is written
onto the recording sheet (namely, the toner image is transferred
onto the recording sheet). Thereafter, the recording sheet passes
through the fixing unit 7, so that unfixed toner on the recording
sheet is molten by heat to be fixed to the recording sheet. Then,
the recording sheet is discharged to the paper output tray 91 via
the carrying roller 12b.
[0068] The carrying path described earlier applies to a case where
a request is made for carrying out single-side printing with
respect to a recording sheet. In contrast, assume that a request is
made for carrying out double-side printing with respect to the
recording sheet. When the carrying roller 12b, which is the last
carrying roller, holds a rear end of the recording sheet which has
passed through the fixing unit 7 and has been subjected to
single-side printing, the carrying roller 12b reversely rotates, so
as to guide the recording sheet to the carrying roller 12c and the
carrying roller 12d.
[0069] Note that a display section (not illustrated) for indicating
information to a user and an instruction input section 41 (see FIG.
1) for receiving an instruction from the user to the image forming
apparatus 100 are provided in the upper part of the apparatus body
110.
[0070] Note here that the image forming apparatus 100 in accordance
with the present embodiment has a plurality of printing modes and
properly uses a plurality of halftone processes in accordance with
the respective plurality of printing modes so that gradation can be
expressed favorably in accordance with the plurality of printing
modes.
[0071] Therefore, the image processing section 20 of the image
forming apparatus 100 carries out a density correction with respect
to the plurality of halftone processes so that density
characteristics such as a printing density and a color tone are
kept constant between the plurality of halftone processes.
[0072] FIG. 1 is a functional block diagram illustrating an
arrangement of the image processing section 20 of the image forming
apparatus 100 in accordance with the present embodiment. The image
processing section 20 includes a halftone process section 38, a
density correction process section 30, a density correction
adjustment section 33, a conversion value table storage section 22,
an output correction value table storage section 23, and a sensor
output value storage section 24. Note that the image processing
section 20 is constituted mainly by a CPU (Central Processing
Unit), a ROM (Read Only Memory), and a RAM (Random Access
Memory).
[0073] The halftone process section 38 carries out a halftone
process in accordance with a function and a mode with respect to
image data. For example, the halftone process section 38 carries
out the following five halftone processes A through E in accordance
with a combination of a function and a mode.
[0074] Halftone process A: dither method.cndot.medium lpi (copy
function--for text and photograph mixture mode)
[0075] Halftone process B: simple quantization method (copy
function--all modes for text region)
[0076] Halftone process C: error diffusion method (copy
function--for text document mode)
[0077] Halftone process D: dither method.cndot.low lpi (copy
function--for photograph mode)
[0078] Halftone process E: dither method.cndot.high lpi (for
printer function)
[0079] In the process control carried out at turn-on or when a
change over time or an environmental change is detected, the
density correction process section 30 carries out a density
correction with respect to the plurality of halftone processes
carried out by the halftone process section 38.
[0080] The density correction process section 30 finds an output
correction value of a reference halftone process in accordance with
a result of actual measurement of densities of respective toner
patches formed on the intermediate transfer belt 61, the reference
halftone process serving as one reference halftone process of the
plurality of halftone processes carried out in the image forming
apparatus 100. The following description may refer to the output
correction value of the reference halftone process found by actual
measurement as a reference output correction value.
[0081] The density correction process section 30 finds output
correction values of halftone processes other than the reference
halftone process (hereinafter referred to as the other halftone
processes) in accordance with the reference output correction value
by conversion by use of a conversion value table (see FIG. 3). The
following description may refer to the output correction values of
the other halftone processes found by conversion from the reference
output correction value as conversion output correction values as
opposed to the reference output correction value.
[0082] According to the present embodiment, the density correction
process section 30 finds an output correction value (a reference
output correction value) by actually measuring a patch density
assuming that the halftone process A, i.e., dither method
.cndot.medium lpi is the reference halftone process, and the
density correction process section 30 finds output correction
values (conversion output correction values) of the halftone
processes B through E by conversion.
[0083] An output correction value table provided in the output
correction value table storage section 23 stores the output
correction values found by the density correction process section
30. The output correction table stores the output correction values
with respect to a given density value for each of the halftone
processes. The halftone process section 38 reads out, from the
output correction table, an output correction value corresponding
to a halftone process to be carried out, so as to carry out the
halftone process.
[0084] The conversion value table storage section 22 stores the
conversion value table. The conversion value table stores
conversion values with respect to a given density value so that the
conversion values correspond to the respective halftone processes
whose output correction values are found by use of conversion
values (specifically described later). The conversion value table
storage section 22 is constituted by, for example, a nonvolatile
memory so that data is held even after the image forming apparatus
100 turns off.
[0085] The sensor output value storage section 24 stores sensor
outputs which the density correction process section 30 uses to
carry out a density correction in accordance with actual
measurement and which serve as a reference for an output
adjustment. How to find the sensor outputs serving as the reference
for the output adjustment is to be described later. The sensor
output value storage section 24 stores values (the sensor outputs)
which are obtained when the sensor 21 (described later) reads patch
densities as much as 15 points indicative of a density
characteristic of the image forming section 42 for each of cyan,
magenta, yellow, and black. The sensor output value storage section
24 is also constituted by a nonvolatile memory since data needs to
be held even after the image forming apparatus 100 turns off.
[0086] The density correction adjustment section 33 receives, from
the instruction input section 41, an instruction to adjust a
density correction process. Then, the density correction adjustment
section 33 reviews the conversion value table which stores the
conversion values (conversion parameters) to be used by the density
correction process section 30 for calculation of output correction
values, so as to adjust the density correction process.
[0087] The following description more specifically discusses the
density correction process section 30 and the density correction
adjustment section 33.
[0088] First, the density correction process section 30 is to be
described. The density correction process section includes an
output correction value actual measurement section 31, an output
correction value conversion section 32, and an internal patch
formation instruction section 34.
[0089] In the process control, in response to an instruction from
the output correction value actual measurement section 31, the
internal patch formation instruction section 34 generates a command
to form an internal patch pattern subjected to the reference
halftone process, so as to give the command to the image forming
section 42.
[0090] According to the present embodiment, in order to adjust the
density correction process, the internal patch formation
instruction section 34 generates a command to form an internal
patch pattern subjected to a halftone process carried out as
instructed from the density correction adjustment section 33, so as
to give the command to the image forming section 42.
[0091] The image forming section 42 which has obtained the command
mainly controls the image forming stations (described earlier) to
form the internal patch pattern on the intermediate transfer belt
61. Note here that a patch which is merely formed on the
intermediate transfer belt 61 but is not printed out is referred to
as an internal patch.
[0092] In the process control, the output correction value actual
measurement section 31 carries out a density correction with
respect to the reference halftone process by actual patch density
measurement, so as to update the output correction value of the
reference halftone process which is stored in the output correction
value table.
[0093] More specifically, the output correction value actual
measurement section 31 instructs the internal patch formation
instruction section 34 to form an internal patch pattern subjected
to the reference halftone process. The sensor 21 reads a patch
density of the internal patch pattern formed on the intermediate
transfer belt 61. From sensor outputs of the sensor 21 which has
read the patch density of the internal patch pattern thus formed,
the output correction value actual measurement section 31
determines a patch which is identical in value to a sensor output
stored in the sensor output storage section 24 and serving as the
reference for the output adjustment, so as to set, to an output
correction value, an output value used to form the determined
patch. The output correction value table stores the output
correction value as the output correction value of the reference
halftone process, that is, the reference output correction
value.
[0094] According to the present embodiment, in a case where the
density correction adjustment section 33 instructs the output
correction value actual measurement section 31 to adjust the
density correction process, the output correction value actual
measurement section 31 carries out the density correction, by
actual patch density measurement, with respect to a halftone
process whose adjustment has been instructed from the density
correction adjustment section 33, so as to calculate, by actual
measurement, an output correction value of the halftone process
whose adjustment has been instructed.
[0095] More specifically, the output correction value actual
measurement section 31 instructs the internal patch formation
instruction section 34 to form an internal patch pattern subjected
to the halftone process whose adjustment has been instructed from
the density correction adjustment section 33. The sensor 21 reads a
patch density of the internal patch pattern formed on the
intermediate transfer belt 61. From sensor outputs of the sensor 21
which has read the patch density of the internal patch pattern thus
formed, the output correction value actual measurement section 31
determines a patch which is identical in value to a sensor output
stored in the sensor output storage section 24 and serving as the
reference for the output adjustment, so as to set, to an output
correction value, an output value used to form the determined
patch. A conversion value calculation section (a first conversion
parameter calculation section or a second conversion parameter
calculation section) 36 (described later) uses the output
correction value to calculate a conversion value.
[0096] The sensor 21 detects densities of respective patches of an
internal patch pattern formed on the intermediate transfer belt 61
(see FIG. 2). According to the present embodiment, the sensor 21
detects, as a toner density, a reflectance of toner from which each
patch is made, so as to supply, to the image processing section 20,
a sensor output in accordance with the reflectance.
[0097] The output correction value conversion section 32 calculates
conversion output correction values which are output correction
values of the halftone processes other than the reference halftone
process by use of (i) the reference output correction value set by
the output correction value actual measurement section 31 and (ii)
the conversion values stored in the conversion value table. The
output correction values of the other halftone processes thus
calculated and the reference output correction value are stored
together in the output correction value table. Note that the output
correction value conversion section 32 can be arranged such that,
when a halftone process to be used is determined, the output
correction value conversion section 32 calculates a conversion
output correction value in accordance with the determined halftone
process, so as to cause the output correction value table to store
the calculated conversion output correction value.
[0098] The following description discusses the density correction
adjustment section 33. The density correction adjustment section 33
includes an actual measurement instruction section 37, a conversion
value calculation section 36, and a conversion value table update
section 39.
[0099] in response to an instruction from the instruction input
section 41 to adjust the density correction process carried out by
the density correction process section 30, the actual measurement
instruction section 37 instructs the output correction value actual
measurement section 31 of the density correction process section 30
to find, by actual measurement, an output correction value of the
halftone process whose adjustment has been instructed.
[0100] Specifically, in response to the instruction to adjust the
density correction process carried out by the density correction
process section 30, the actual measurement instruction section 37
instructs the output correction value actual measurement section 31
to carry out a density correction, by actual patch density
measurement, with respect to the halftone process whose adjustment
has been instructed, so as to find an output correction value by
actual measurement. Namely, the actual measurement instruction
section 37 and the output correction value actual measurement
section 31 constitute the first output correction value actual
measurement section and the second output correction value actual
measurement section of the present invention.
[0101] In a case where the halftone process whose adjustment has
been instructed belongs to the halftone processes other than the
reference halftone process, the conversion value calculation
section 36 calculates a new conversion parameter for the halftone
process in accordance with (i) the output correction value of the
halftone process found by the output correction value actual
measurement section 31 by actual measurement and (ii) the reference
output correction value stored in the output correction value table
(functions as the first conversion parameter calculation section).
Note here that the reference output correction value stored in the
output correction value table has been updated in the process
control carried out by the density correction process section
30.
[0102] After the conversion value calculation section 36 has
calculated a new conversion value, the conversion value table
update section 39 accesses the conversion value table storage
section 22, so as to update the conversion value set for the
halftone process whose adjustment has been instructed to the
conversion value which has been newly calculated by the conversion
value calculation section 36 (functions as the first conversion
parameter update section).
[0103] The output correction value, stored in the output correction
value table, of the halftone process whose adjustment has been
instructed is also rewritten to the output correction value found
by the output correction value actual measurement section 31 so
that the conversion value is reviewed.
[0104] In a case where the halftone process whose adjustment has
been instructed is the reference halftone process, for all the
halftone processes having conversion values, the conversion value
calculation section 36 calculates new conversion values in
accordance with (i) an output correction value (a new reference
output correction value) of the reference halftone process found by
the output correction value actual measurement section 31 by actual
measurement but not in the process control, (ii) the reference
output correction value stored in the output correction value
table, and (iii) the conversion value stored in the conversion
value table (functions as the second conversion parameter
calculation section).
[0105] Note here that the conversion value calculation section 36
calculates the new conversion values so that an output correction
value found by conversion from the output correction value of the
reference halftone process found by the output correction value
actual measurement section 31 by actual measurement in response to
the adjustment instruction but not in the process control is
identical in value to an output correction value found by
conversion from the output correction value of the reference
halftone process stored in the output correction value table.
[0106] After the conversion value calculation section 36 has
calculated the new conversion values for all the halftone processes
having conversion values, the conversion value table update section
39 accesses the conversion value table storage section 22, so as to
update the conversion values set for all the halftone processes
having conversion values to the conversion values which have been
newly calculated by the conversion value calculation section 36
(functions as the second conversion parameter update section).
[0107] As described earlier, in a case where an output correction
value of the reference halftone process is newly found in the
density correction adjustment but not in the process control, the
reference output correction value stored in the output correction
value table is also updated.
[0108] Namely, in response to the instruction to adjust the
reference halftone process, the density correction adjustment
section 33 newly finds a reference output correction value so as to
update the reference output correction value stored in the output
correction value table, and recalculates the conversion values of
all the halftone processes stored in the conversion value table so
that conversion values of the other halftone processes which have
been obtained by conversion from the new output correction value of
the reference halftone process are identical to output correction
values obtained by conversion from the reference output correction
value which is old and has not been updated.
[0109] The following description specifically discusses processes
carried out in the image processing section 20 and including the
density correction adjustment process carried out by the density
correction adjustment section 33.
[0110] First, how to prepare a conversion value table is to be
described. Note that it is desirable to set a conversion value
table for each image forming apparatus so that an individual
difference between apparatuses can be absorbed. However, a common
conversion value table prepared in accordance with actual
measurement is commonly preliminarily set for image forming
apparatuses of an identical model.
[0111] FIG. 3 illustrates an example of the conversion value table.
In the example of FIG. 3, the reference output correction value
which is the output correction value of the reference halftone
process (hereinafter referred to as a reference halftone process A)
and serves as a reference for calculation of a conversion value is
stored in a first tier of the conversion value table. Conversion
values of the other halftone processes (hereinafter referred to as
the other halftone processes B through E) are stored in second
through fifth tiers of the conversion value table.
[0112] In order to make it easy to understand how output correction
values are calculated by use of conversion values, FIG. 3 shows the
example as if the reference output correction value was also stored
in the conversion value table. However, what is described in the
first tier shows the reference output correction value stored in
the output correction value table.
[0113] Note that it is not necessarily required that a conversion
value table preparation section (not illustrated) be provided in
the image processing section 20. Alternatively, a conversion value
table commonly set for image forming apparatuses of an identical
model can be initially set for the conversion value table storage
section 22.
[0114] The conversion value table preparation section causes the
image forming section 42 to print a patch set (see FIG. 4) on a
recording sheet in a state where no output adjustment is carried
out. The patch set forms a plurality of patches for each of cyan,
magenta, yellow, and black. According to the present embodiment,
since a density value indicative of the density characteristic of
the image forming section 42 is set to 15 points, 32 patches which
are sufficiently more than 15 points are formed for each of the
colors. Note here that data on the patch set can be preliminarily
stored in the image forming apparatus 100 or can be received from
an external PC. The document reading device 90 (see FIG. 2) reads
the recording sheet thus printed.
[0115] From a result of reading by the document reading device 90
of the patch set which has been printed on the recording sheet, the
conversion value table preparation section selects, for each of the
colors, 15 patches which correspond to the density value of 15
points that are suitable for defining a curved line and indicative
of the density characteristic of the image forming section 42.
Then, the conversion value table preparation section causes the
selected 15 patches to be formed on the intermediate transfer belt
61, so as to cause the sensor to read reflectances (densities) of
the respective patches. The sensor output value storage section 24
stores the reflectances of the respective patches read here as
sensor output values serving as the reference for the output
adjustment. The sensor output values which are stored in the sensor
output value storage section 24 and correspond to the reflectances
of the respective patches thus serve as a reference for a density
correction to be carried out in a subsequent process control.
[0116] Next, the conversion value table preparation section
instructs the internal patch formation instruction section 34 to
form an internal patch pattern subjected to the reference halftone
process A. From sensor outputs of the sensor 21 which has read a
patch density of the internal patch pattern formed on the
intermediate transfer belt 61, the conversion value table
preparation section determines a patch which is identical in value
to a sensor output value stored in the sensor output storage
section 24 and serving as the reference for the output adjustment,
so as to set, to a reference output correction value, an output
value used to form the determined patch. The output correction
value table stores the reference output correction value.
[0117] For example, in a case where a density of a patch formed by
the reference halftone process A when an input value is "118" is
identical to a density of a patch formed when an input value stored
in the sensor output value storage section 24 is "128", a
registered output correction value of the reference halftone
process A is set to "118" with respect to the input value of
"128".
[0118] Similarly, the conversion value table preparation section
causes the internal patch formation instruction section 34 to form
internal patch patterns subjected to the other halftone processes B
through E, so as to find, also by actual measurement, output
correction values of the other halftone processes B through E. In
this case, differently from the case of the reference halftone
process A, the output correction values of the other halftone
processes B through E found by actual measurement are not stored as
they are but are stored in the form of conversion values with
respect to the reference output correction value of the reference
halftone process A.
[0119] In the example of the conversion value table of FIG. 3, a
ratio to the reference output correction value is stored as a
conversion value for the halftone process B.
[0120] Differences from the reference output correction value are
stored as conversion values for the halftone processes C through E.
Equations (1) and (2) by which a conversion value is calculated are
described below.
[0121] When a conversion value is a ratio:
conversion value (ratio)=output correction value of other halftone
process found by actual measurement/reference output correction
value of reference halftone process (1)
[0122] When a conversion value is a difference:
conversion value (difference)=output correction value of other
halftone process found by actual measurement-reference output
correction value of reference halftone process (2)
[0123] FIG. 5 illustrates an example of a program for calculating a
conversion value to be stored in the conversion value table. For
example, a program as illustrated in FIG. 5 enables calculation of
a conversion value.
[0124] The conversion value table in which the conversion values of
the other halftone processes B through E are stored are thus
prepared so that conversion output correction values are calculated
by use of the reference output correction value of the reference
halftone process A.
[0125] The following description discusses the density correction
process carried out in the process control at turn-on or when a
change over time or an environmental charge is detected.
[0126] in the process control, in response to the instruction from
the output correction value actual measurement section 31, the
internal patch formation instruction section 34 generates a command
to form the internal patch pattern subjected to the reference
halftone process A, so as to give the command to the image forming
section 42. The image forming section 42 which has obtained the
command mainly controls the image forming stations (described
earlier) to form the internal patch pattern on the intermediate
transfer belt 61.
[0127] The sensor 21 reads a patch density of the internal patch
pattern thus formed. From sensor outputs of the sensor 21 which has
read the patch density of the internal patch pattern thus formed,
the output correction value actual measurement section 31
determines a patch which is identical in value to a sensor output
value stored in the sensor output storage section 24 and serving as
the reference for the output adjustment. Then, the output
correction value actual measurement section 31 sets, to an output
correction value, an output value used to form the determined
patch, so as to update the reference output correction value of the
reference halftone process stored in the output correction value
table.
[0128] In response to the update to the reference output correction
value stored in the output correction value table, the output
correction value conversion section 32 calculates conversion output
correction values of the other halftone processes B through E by
use of the updated reference output correction value and the
conversion values stored in the conversion value table, so as to
update the output correction values of the other halftone processes
B through E stored in the output correction value table. Equations
(3) and (4) by which a conversion output correction value is
calculated are described below.
[0129] When a conversion value is a ratio:
conversion output correction value=updated reference output
correction value.times.conversion value stored in conversion value
table (3)
[0130] When a conversion value is a difference:
conversion output correction value=updated reference output
correction value+conversion value stored in conversion value table
(4)
[0131] As described earlier, the density correction process section
30 forms an internal patch pattern for only the reference halftone
process A, so as to calculate an output correction value by actual
patch density measurement. The density correction process section
30 calculates, by conversion, conversion correction values for the
other halftone processes B through E without forming internal patch
patterns. This enables a reduction in printing material and
processing time.
[0132] The following description discusses the density correction
adjustment process in which the density correction process is
adjusted by reviewing the conversion values stored in the
conversion value table. As described earlier, in the common density
correction process carried out in the process control or the like,
the density correction is carried out with respect to the other
halftone processes B through E by calculating output correction
values by conversion.
[0133] However, in a case where a conversion value is fixed and
density characteristics of the halftone processes A through E
change over time or a property of an apparatus is not in conformity
with a commonly set conversion value, a density characteristic
assumed when the conversion value is set and an actual density
characteristic may not match.
[0134] According to the image processing section 20 in accordance
with the present embodiment, for example, in a case where a density
abnormality occurs in a printed image due to a change over time in
density characteristics of the other halftone processes B through
E, the density correction adjustment section 33 receives an
instruction from the user, so as to rewrite, in accordance with the
instruction, conversion values which (i) are associated with the
other halftone processes in which the density abnormality has
occurred and (ii) are stored in the conversion value table.
[0135] FIG. 6 is a flow chart illustrating how the image processing
section 20 carries out the density correction adjustment process
when the density adjustment instruction is given to the other
halftone processes. For example, in a case where a density
abnormality occurs in the halftone process C, which is one of the
other halftone processes, the user inputs, into the instruction
input section 41, the instruction to carry out the density
correction adjustment with respect to the halftone process C (S1)
(see FIG. 6).
[0136] When the density correction adjustment section 33 receives
the instruction inputted at S1, the actual measurement instruction
section 37 gives the instruction to the internal patch formation
instruction section 34 via the output correction value actual
measurement section 31. The internal patch formation instruction
section 34 generates a command to form an internal patch pattern
subjected to the halftone process C, so as to give the command to
the image forming section 42. The image forming section 42 which
has obtained the command mainly controls the image forming stations
to form, on the intermediate transfer belt 61, the internal patch
pattern subjected to the halftone process C (S2).
[0137] The sensor 21 detects a patch density of the internal patch
pattern formed on the intermediate transfer belt 61 at S2 (S3). The
density correction adjustment section 33 retrieves a patch which is
identical in density to each patch detected by the sensor and is
stored in the sensor output value storage section 24, so as to
determine, as a correct output correction value of the halftone
process C, an output value used to form the retrieved patch (S4).
Then, the conversion value calculation section 36 and the
conversion value table update section 39 of the density correction
adjustment section 33 rewrite the conversion values in accordance
with the new output correction value thus determined (S5).
Equations (5) and (6) by which the conversion values of the other
halftone processes are reviewed are described below.
[0138] When a conversion value is a ratio:
new conversion value (ratio)=new output correction value of other
halftone process found by actual measurement/reference output
correction value of reference halftone process (5)
[0139] When a conversion value is a difference:
new conversion value (difference)=new output correction value of
other halftone process found by actual measurement-reference output
correction value of reference halftone process (6)
[0140] As described above, an output correction value of the
halftone process C whose adjustment in the output correction value
table has been instructed is also rewritten when the density
correction adjustment process is carried out. Note here that the
output correction value can be rewritten in the output correction
value table by using a new output correction value found by actual
measurement as it is or by recalculating a conversion output
correction value by use of a new conversion value.
[0141] As described earlier, in a case where a conversion value is
rewritten for each of the other halftone processes in which an
abnormality occurs, it is possible to carry out a density
correction more properly in accordance with a change over time in
density characteristic of a halftone process and/or an individual
difference between apparatuses, as compared with a conventional
case in which a density correction is carried out by use of a
conversion value which is not rewritten and is fixed.
[0142] Therefore, according to the image processing section 20, it
is possible to make the image forming apparatus 100 which (i)
prevents a reduction in accuracy with which a density correction is
carried out by conversion with respect to a halftone process and
(ii) enables expression of proper halftone.
[0143] The following description discusses how the density
adjustment process is carried out when the density adjustment
instruction is given to the reference halftone process.
[0144] FIG. 7 is a flow chart illustrating how the image processing
section 20 carries out the density correction adjustment process
when the density adjustment instruction is given to the reference
halftone process. In a case where a density abnormality occurs in
the reference halftone process A, the user inputs, into the
instruction input section 41, the instruction to carry out the
density correction adjustment with respect to the reference
halftone process A (S11) (see FIG. 7).
[0145] When the density correction adjustment section 33 receives
the instruction inputted at S11, the actual measurement instruction
section 37 gives the instruction to the internal patch formation
instruction section 34 via the output correction value actual
measurement section 31. The internal patch formation instruction
section 34 generates a command to form an internal patch pattern
subjected to the reference halftone process A, so as to give the
command to the image forming section 42. The image forming section
42 which has obtained the command mainly controls the image forming
stations to form, on the intermediate transfer belt 61, the
internal patch pattern subjected to the halftone process A
(S12).
[0146] The sensor 21 detects a patch density of the internal patch
pattern formed on the intermediate transfer belt 61 at S12 (S13).
The density correction adjustment section 33 retrieves a patch
which is identical in density to each patch detected by the sensor
and is stored in the sensor output value storage section 24, so as
to determine, as a correct output correction value of the reference
halftone process A, an output value which is used to form the
retrieved patch (S14). Then, the conversion value calculation
section 36 and the conversion value table update section 39 of the
density correction adjustment section 33 rewrite the reference
output correction value stored in the output correction value table
(S15), and rewrite the conversion values of the other halftone
processes B through E in accordance with the new reference output
correction value thus determined (S16).
[0147] Equations (7) and (8) by which the conversion values of the
other halftone processes are reviewed are described below.
[0148] When a conversion value is a ratio:
new conversion value=old conversion value.times.old reference
output correction value/new reference output correction value
(7)
[0149] When a conversion value is a difference:
new conversion value=old conversion value+old reference output
correction value-new reference output correction value (8)
[0150] As described above, in a case where the density adjustment
instruction is given to the reference halftone process A and the
reference output correction value is reviewed, the density
correction adjustment section 33 calculates new conversion values
by use of the equations (7) and (8) so that the output correction
values calculated by conversion by the output correction value
conversion section 32 are identical before and after the reference
output correction value is rewritten. Then, the conversion value
table update section 39 rewrites the conversion value table in
accordance with the new conversion values.
[0151] According to this, it is possible to respond to a density
abnormality in the reference halftone process A while maintaining
the output correction values of the other halftone processes B
through E.
[0152] As described earlier, according to the image processing
section 20 in accordance with the present embodiment, the density
correction adjustment section 33 can review, in accordance with the
instruction from the user, the conversion value table stored in the
conversion value table storage section 22. Therefore, it is
possible to carry out a density correction more properly in
accordance with a change over time in density characteristics of
the other halftone processes B through E and/or an individual
difference between apparatuses, as compared with a conventional
case in which a density correction is carried out by use of a
conversion value which cannot be rewritten and is fixed.
[0153] Therefore, according to the image processing section 20, it
is possible to make the image forming apparatus 100 which enhances
an accuracy with which a density correction is carried out by
conversion with respect to a halftone process.
[0154] Note that the present embodiment uses a conversion value
table in which a conversion parameter is a conversion value.
However, the present invention is not limited to this. For example,
an arithmetic expression can be used as the conversion
parameter.
Second Embodiment
[0155] A second embodiment of the present invention is described
below with reference to FIGS. 8 and 9. The present embodiment is to
discuss an image forming apparatus which carries out a plurality of
halftone processes, the image forming apparatus being arranged such
that the number of reference halftone processes is not set to one
and the image forming apparatus includes an image processing
section which can change the reference halftone processes according
to need.
[0156] Note that for convenience, members having functions
identical to those of the respective members illustrated in the
drawings of the First Embodiment are given respective identical
reference numerals, and a description of those members is omitted
here.
[0157] The First Embodiment discussed a case where in the image
forming apparatus 100 which carries out a plurality of halftone
processes, a density correction is carried out by setting one of
the plurality of halftone processes as a reference halftone process
and appropriately rewriting conversion values of the other halftone
processes.
[0158] However, a change of reference halftone processes enables an
output adjustment which is more suitable for a user's mode of use.
For example, in a case where one of the plurality of halftone
processes which is used most frequently is changed to a reference
halftone process, it is possible to more properly express halftone
of an image formed by the reference halftone process.
[0159] FIG. 8 is a block diagram illustrating an example of an
arrangement of an image processing section 120 in accordance with
the present embodiment. The image processing section 120 further
includes a counter (a counting section) 25 and a reference halftone
process changing section 35 in addition to members of the image
processing section 20 described in the First Embodiment.
[0160] The counter 25 measures a frequency of use of the plurality
of halftone processes in a given period.
[0161] The reference halftone process changing section 35 selects a
halftone process from the plurality of halftone processes and
changes the selected halftone process to a reference halftone
process in accordance with an instruction from the user or the
frequency of use measured by the counter 25.
[0162] Note that the other members of the image processing section
120 are identical to those of the image processing section 20
described in the First Embodiment and a description thereof is
omitted here.
[0163] The following description discusses how the image processing
section 120 carries out the reference halftone process changing
process. Note that as in the case of the First Embodiment, the
image forming apparatus of the present embodiment is arranged such
that five halftone processes A through E are carried out and the
halftone process A is set as a reference halftone process.
[0164] FIG. 9 is a flow chart illustrating how the image processing
section 120 carries out the reference halftone process changing
process. First, the reference halftone process changing section 35
determines a frequency of use of the halftone processes A through E
in a given period, the frequency having been measured by the
counter 25 (S31) (see FIG. 9).
[0165] In accordance with the frequency of use determined at S31,
the reference halftone process changing section 35 selects, as a
reference halftone process, a halftone process which is used most
frequently (S32).
[0166] Next, the reference halftone process changing section 35
determines whether or not it is necessary to rewrite the reference
halftone process (S33), Specifically, the image processing section
120 determines whether or not a reference halftone process set at
the time of the determination by the reference halftone process
changing section 35 and the halftone process selected at S32 are
identical (S33).
[0167] In a case where it is unnecessary to rewrite the reference
halftone process (NO at S33), i.e., in a case where the reference
halftone process set at the time of the determination by the
reference halftone process changing section 35 and the reference
halftone process selected at S32 are identical, the reference
halftone process changing section 35 finishes carrying out the
reference halftone process changing process.
[0168] In contrast, in a case where it is necessary to rewrite the
reference halftone process (YES at S33), i.e., in a case where the
reference halftone process set at the time of the determination by
the reference halftone process changing section 35 and the
reference halftone process selected at S32 are not identical, the
reference halftone process changing section 35 rewrites a reference
output correction value stored in a conversion value table (S34).
For example, in a case where the halftone process C is used most
frequently, the reference halftone process changing section 35 sets
the halftone process C as a new reference halftone process instead
of the halftone process A, so as to rewrite the conversion value
table.
[0169] Specifically, the reference halftone process changing
section 35 calculates a reference output correction value of the
halftone process C by calculating a difference between a reference
output correction value (an output correction value table) of the
halftone process A and a conversion value (the conversion value
table) of the halftone process C.
[0170] Next, the reference halftone process changing section 35 not
only sets a conversion value of the halftone process A but also
rewrites conversion values (S35). Specifically, the reference
halftone process changing section 35 rewrites the conversion values
by calculating conversion values with respect to the reference
output correction value of the halftone process C for the other
halftone processes A, B, D, and E. A process carried out in this
case is substantially identical to that carried out at S16 in the
flow chart illustrated in FIG. 7.
[0171] As described earlier, according to the image processing
section 120 in accordance with the present embodiment, it is
possible to not only review registered conversion values but also
change reference halftone processes. Therefore, a density
correction is carried out in which a halftone process that is used
most frequently by the user is a reference halftone process. This
allows implementation of an optimum density correction process in
accordance with a user's mode of use.
[0172] Note that, though the present embodiment discussed an
arrangement in which a halftone process that is used most
frequently is selected to be changed to a reference halftone
process, the present invention is not limited to this. For example,
the present invention can be arranged such that reference halftone
processes are not changed in a case where a difference between a
frequency of use of a reference halftone process set at the time of
determination whether or not it is necessary to rewrite the
reference halftone process and a frequency of use of the halftone
process that is used most frequently is less than a threshold which
is separately set.
[0173] Note also that, though the present embodiment discussed an
arrangement in which the counter 25 is provided and reference
halftone processes are changed in accordance with a frequency of
use measured by the counter 25, the present invention is not
limited to this. For example, the present invention can be arranged
such that no counter 25 is provided and a reference halftone
process changing process is carried out in accordance with a
reference halftone process changing instruction inputted into an
instruction input section 41.
Summary of Embodiments
[0174] The image forming apparatus in accordance with the
embodiments having a function of carrying out a plurality of
halftone processes, the image forming apparatus includes: a density
correction process section for carrying out a density correction
process with respect to the plurality of halftone processes; and a
density correction adjustment section for adjusting the density
correction process carried out by the density correction process
section, the density correction process section finding an output
correction value of a reference halftone process of the plurality
of halftone processes by use of a result of measurement of
densities of respective patches of a patch pattern subjected to the
reference halftone process, and finding an output correction value
of at least one of the plurality of halftone processes which is
other than the reference halftone process by conversion from the
output correction value of the reference halftone process by use of
a conversion parameter set for the at least one halftone process,
the density correction adjustment section receiving an instruction
to adjust the density correction process carried out by the density
correction process section and reviewing the conversion parameter
used by the density correction process section, so as to adjust the
density correction process.
[0175] According to the arrangement, the density correction
adjustment section receives an instruction to adjust the density
correction process carried out by the density correction process
section and reviews the conversion parameter used by the density
correction process section, so as to adjust the density correction
process.
[0176] According to this, also for a halftone process using a
conversion parameter, the conversion parameter can be reviewed
properly in accordance with a change over time in density
characteristic of the halftone process and/or an individual
difference between apparatuses. This enables enhancement of a
density correction accuracy.
[0177] Therefore, according to the embodiments, it is possible to
make an image processing apparatus which carries out a density
correction process with higher accuracy even by use of conversion
as compared with a conventional arrangement in which a density
correction process is carried out by use of a conversion parameter
(a conversion value or a conversion expression) which cannot be
rewritten and is fixed.
[0178] The image processing apparatus in accordance with the
embodiments can be arranged such that: the density correction
adjustment section includes: a first output correction value actual
measurement section for, in response to an instruction to adjust a
halftone process of the plurality of halftone processes which is
other than the reference halftone process, finding an output
correction value of the halftone process by use of a result of
measurement of densities of respective patches of a patch pattern
subjected to the halftone process whose adjustment has been
instructed; a first conversion parameter calculation section for,
in accordance with (i) the output correction value found by the
first output correction value actual measurement section and (ii)
the output correction value of the reference halftone process
already found by the density correction process section, finding a
new conversion parameter for the halftone process whose adjustment
has been instructed; and a first conversion parameter update
section for updating a conversion parameter of the halftone process
whose adjustment has been instructed to the new conversion
parameter calculated by the first conversion parameter calculation
section.
[0179] According to the arrangement, in response to an instruction
to adjust a halftone process of the plurality of halftone processes
which is other than the reference halftone process, a first output
correction value actual measurement section gives an instruction to
form a patch pattern subjected to the halftone process whose
adjustment has been instructed, so as to find an output correction
value of the halftone process by actual measurement.
[0180] After the output correction value has been found by actual
measurement, in accordance with (i) the output correction value
found by actual measurement and (ii) the output correction value of
the reference halftone process already found by the density
correction process section, a first conversion parameter
calculation section finds a new conversion parameter for the
halftone process whose adjustment has been instructed, and a first
conversion parameter update section updates a conversion parameter
of the halftone process whose adjustment has been instructed to the
new conversion parameter calculated by the first conversion
parameter calculation section.
[0181] According to this, it is possible to easily make an image
processing apparatus in which for a halftone process using a
conversion parameter to carry out a density correction process, the
conversion parameter can be reviewed properly in accordance with a
change over time in density characteristic of the halftone process
and/or an individual difference between apparatuses in response to
an instruction to adjust the density correction process carried out
by the halftone process.
[0182] The image processing apparatus in accordance with the
embodiments can be arranged such that: the density correction
adjustment section includes: a second output correction value
actual measurement section for, in response to an instruction to
adjust the reference halftone process of the plurality of halftone
processes, finding an output correction value of the reference
halftone process by use of the result of the measurement of the
densities of the respective patches of the patch pattern subjected
to the reference halftone process; a second conversion parameter
calculation section for finding new conversion parameters for all
the halftone processes having conversion parameters in accordance
with (i) the output correction value of the reference halftone
process found by the second output correction value actual
measurement section, (ii) the output correction value of the
reference halftone process already found by the density correction
process section, and (iii) predetermined conversion parameters so
that an output correction value found by conversion from the output
correction value of the reference halftone process found by the
second output correction value actual measurement section is
identical to an output correction value found by conversion from
the output correction value of the reference halftone process
already found by the density correction process section; and a
second conversion parameter update section for updating the
conversion parameters of all the halftone processes to the new
conversion parameters calculated by the second conversion parameter
calculation section.
[0183] According to the arrangement, in response to an instruction
to adjust the reference halftone process of the plurality of
halftone processes, a second output correction value actual
measurement section gives an instruction to form a patch pattern
subjected to the reference halftone process, so as to find an
output correction value of the reference halftone process by actual
measurement.
[0184] After the output correction value of the reference halftone
process has been found by actual measurement, a second conversion
parameter calculation section finds new conversion parameters for
all the halftone processes having conversion parameters in
accordance with (i) the output correction value of the reference
halftone process found by the second output correction value actual
measurement section, (ii) the output correction value of the
reference halftone process already found by the density correction
process section, and (iii) predetermined conversion parameters, and
a second conversion parameter update section updates the conversion
parameters of all the halftone processes to the new conversion
parameters calculated by the second conversion parameter
calculation section.
[0185] Note here that the second conversion parameter calculation
section finds the new conversion parameters so that an output
correction value found by conversion from the output correction
value of the reference halftone process found by the second output
correction value actual measurement section is identical to an
output correction value found by conversion from the output
correction value of the reference halftone process already found by
the density correction process section.
[0186] According to this, in a case where an adjustment instruction
is given to the reference halftone process, it is possible to
adjust only the density correction process carried out by the
reference halftone process while conversion parameters of the other
halftone processes, which do not need to be adjusted, are rewritten
so that output values of the other halftone processes remain
unchanged before and after the reference halftone process is
adjusted.
[0187] The image forming apparatus in accordance with the
embodiments can be arranged to further include a reference halftone
process changing section which enables a change of reference
halftone processes in the density correction process section.
[0188] According to the arrangement, a reference halftone process
changing section enables a change of reference halftone processes
in the density correction process section. Therefore, it is
possible to not only review a conversion parameter but also change,
in accordance with user's needs, reference halftone processes in
which a density correction process is carried out in accordance
with actual measurement.
[0189] The image forming apparatus in accordance with the
embodiments can be arranged to further include: a counting section
for measuring a frequency of use, in a given period, of the
plurality of halftone processes, each being a possible reference
halftone process, the reference halftone process changing section
setting, as a reference halftone process, a halftone process of the
plurality of halftone processes whose frequency of use measured by
the counting section is the highest.
[0190] According to the arrangement, a counting section measures a
frequency of use, in a given period, of the plurality of halftone
processes, each being a possible reference halftone process, and
the reference halftone process changing section sets a halftone
process of the plurality of halftone processes whose frequency of
use is the highest as a reference halftone process whose output
correction value is found by the density correction process section
by use of a result of measurement of densities of respective
patches of a patch pattern.
[0191] This allows a density correction process to be carried out
in accordance with actual measurement with respect to a halftone
process which is used by the user most frequently. Therefore, it is
possible to carry out a density correction process which further
meets user's needs.
[0192] The image forming apparatus in accordance with the
embodiments can be arranged such that the conversion parameter is a
conversion value. The image forming apparatus in accordance with
the embodiments can be arranged such that the conversion value is a
difference from or a ratio to the output correction value of the
reference halftone process.
[0193] An image forming apparatus includes an image processing
apparatus mentioned above.
[0194] According to the arrangement, it is possible to make an
image forming apparatus in which a density correction is carries
out with higher accuracy in a halftone process using
conversion.
[0195] Note that it is possible to cause a computer to implement an
image processing apparatus mentioned above. In this case, (i) a
program for causing the computer to implement a multifunction
printer by causing the computer to operate as each section of the
image processing apparatus and (ii) a computer-readable recording
medium in which the program is recorded are both encompassed in the
scope of the present embodiment.
[0196] The present invention is not limited to the description of
the embodiments above, but may be altered by a skilled person
within the scope of the claims. An embodiment based on a proper
combination of technical means disclosed in different embodiments
is encompassed in the technical scope of the present invention.
[0197] Finally, each block of an image processing apparatus and an
image forming apparatus can be implemented by a hardware logic or
by software by use of a CPU as below.
[0198] Namely, each of an image processing apparatus and an image
forming apparatus includes (i) a CPU (central processing unit)
which executes a command of a control program that implements each
function of the image processing apparatus and the image forming
apparatus, (ii) a ROM (read only memory) in which the control
program is stored, (iii) a RAM (random access memory) which
extracts the control program, (iv) a storage device (a recording
medium) such as a memory in which the control program and various
sets of data are stored, and (v) the like. The object of the
present invention is attainable by supplying, to the image
processing apparatus and the image forming apparatus, a recording
medium in which program codes (an executable program, an
intermediate code program, and a source program) of a control
program of a density correction process section 30 which is
software that implements the each function are computer-readably
recorded and causing a computer (or a CPU or an MPU) of each of the
image processing apparatus and the image forming apparatus to read
out and carry out the program codes recorded in the recording
medium.
[0199] Examples of the recording medium include (i) tapes such as a
magnetic tape and a cassette tape, (ii) disks including magnetic
disks such as a Floppy (Registered Trademark) disk and a hard disk,
and optical disks such as a CD-ROM, an MO, an MD, a DVD, and a
CD-R, (iii) cards such as an IC card (including a memory card) and
an optical card, and (iv) semiconductor memories realized by a mask
ROM, EPROM, EEPROM, a flash ROM, and the like.
[0200] Each of the image processing apparatus and, the image
forming apparatus can be connected to a communication network, via
which the program codes can be supplied to the image processing
apparatus and the image forming apparatus. Such a communication
network is not particularly limited. Examples of the communication
network includes the Internet, an intranet, an extranet, a LAN,
ISDN, VAN, a CATV communications network, a virtual private
network, a telephone network, a mobile telecommunications network,
and a satellite communication network. A transmission medium of
which a communication network is composed is not particularly
limited. Examples of the transmission medium includes wired
transmission media such as IEEE1394, a USB, a power-line carrier, a
cable TV circuit, a telephone line, and ADSL and wireless
transmission media such as infrared communication systems such as
IrDA and a remote controller, Bluetooth (Registered Trademark),
802.11 wireless communication system, HDR, a mobile phone network,
a satellite circuit, and a digital terrestrial network. Note that
the present invention can also be realized in a form of a computer
data signal in which the program codes are embodied by an
electronic transmission and which is embedded in carrier waves.
INDUSTRIAL APPLICABILITY
[0201] The present invention can be used for various image forming
apparatuses such as a multifunction printer (MFP).
REFERENCE SIGNS LIST
[0202] 20 Image processing section (Image processing apparatus)
[0203] 22 Conversion value table storage section [0204] 23 Output
correction value table storage section [0205] 24 Sensor output
value storage section [0206] 25 Counter (Counting section) [0207]
30 Density correction process section (Density Correction Process
Section) [0208] 31 Output correction value actual measurement
section (First output correction value actual measurement section,
Second output correction value actual measurement section) [0209]
32 Output correction value conversion section [0210] 33 Density
correction adjustment section (Density correction adjustment
section) [0211] 34 Internal patch formation instruction section
[0212] 35 Reference halftone process changing section (Reference
halftone process changing section) [0213] 36 Conversion value
calculation section [0214] 37 Actual measurement instruction
section (First output correction value actual measurement section,
Second output correction value actual measurement section) [0215]
38 Halftone process section [0216] 39 Conversion value table update
section (Conversion Parameter Update Section) [0217] 100 Image
forming apparatus [0218] 120 Image processing section (Image
processing apparatus)
* * * * *